Various physical effects come into consideration for a direct and contact-free metering of a flow of gaseous media. With a thermal method, the cooling down of a heating resistor arranged in a measuring bridge caused by the medium is sensed and evaluated. In case a Coanda nozzle is used, a pressure difference caused by the flow is measured and evaluated. A further possibility is the Vortex method in which eddies are generated by having a flow of a medium along a perturbation body, the frequency offset, which is caused by the eddies, of an acoustic signal being measured which is transmitted transverse to the direction of flow. Each of these methods has its advantages and disadvantages. The former methods have a somewhat long response time with respect to changes in flow and are only suitable for relatively small flow rates (thermal method) or relatively high ones (Coanda nozzle method). The latter method is difficult from the aspect of measurement technology, because the changes in frequency, caused by the eddies, are very small and the wanted signal has a very low amplitude in relation to the excitation signal which in fact is transferred directly to the receiver through the corpus of the measuring chamber.
Nevertheless, the invention makes use of the Vortex method for which it suggests a particularly advantageous signal evaluation.